(1) Field of the Invention
The present invention relates to improved dry-set mortar compositions which contain an organic material which functions as a water retentivity promoter with the other components of the dry-set mortar to yield improved water retentivity not heretofore obtained.
(2) Description of the Prior Art
Dry-set mortars are recognized in the art as compositions distinguished from other hydraulic cement compositions. Conventional mortars generally contain a hydraulic cement, such as Portland cement, sand and water. The hydraulic cement component requires water in order to cure or harden. As a result, conventional mortars are not entirely self-curing because they tend to lose considerable amounts of water by evaporation into the surrounding air and also by absorption into the tile or masonry being set. Where the water loss is too great, the curing action is incomplete and the mortar becomes soft and chalky.
By increasing the proportion of water in the mortar to counteract the water loss, the mortar becomes too thin to work properly. A high water to mortar ratio also leads to cracking due to excessive shrinking of the mortar during curing. To insure sufficient water for hardening conventional mortars, wet conditions must be maintained on the substrate over which the mortar is placed and in the atmosphere surrounding the area during the period of curing. For example, where non-vitreous, absorbent tile are set, the loss of water is even greater, often requiring the non-vitreous tile to be soaked before being set.
Dry-set mortars are distinguished from conventional cementitious compositions because they additionally contain water retentive agents which tend to prevent the loss of substantial amounts of water from the mortar to the surroundings during the curing stages. As used herein, the term "dry-set mortar" is used in its broadest sense to include a mixture of a hydraulic cement such as Portland cement, with additives imparting water retentivity. Such cementitious compositions may be used as a coating, adhesive, mortar or grout adjacent such materials as plumb and true masonry, concrete, cut-cell expanded polystyrene, or rigid closed-cell, urethane insulation board, gypsum board, concrete glass fiber re-enforced backer board, lean Portland cement mortar and more conventional wall and floor setting beds, brick, ceramic tile, marble and stucco. Dry-set mortars have been described, for example, in U.S. Pat. Nos. 2,820,713; 2,934,932; 2,990,382; 3,030,258; and 3,243,307.
The materials which have generally been added to dry-set mortars to improve water retentive properties have been high molecular weight materials which generally increase the viscosity of the liquid phase of the mortar mixture. It has been thought that water retentivity does correspond on a one to one basis with improvement in the viscosity of the liquid phase of the mortar mixture. Therefore, water retentive agents have generally fallen into the category of high molecular weight thickeners of the water-soluble type wherein they thicken or increase the viscosity of the aqueous phase of the dry-set mortar mixture.
In U.S. Pat. No. 3,030,258, a dry-set mortar is described having excellent water retentive properties when it contains a methyl cellulose of 10 to 7,000 cps. viscosity grade in two percent solution in quantities of 0.2 to 6.5% based on the dry weight of the composition. In U.S. Pat. No. 3,243,307, hydroxyethyl cellulose is taught as more effective than methyl cellulose because less hydroxyethyl cellulose is required to obtain the same water retentive properties. The greater effectiveness of the hydroxyethyl cellulose can be attributed to its higher viscosity, described in that patent as 400 to 30,000 cps. in two percent solution.
Although water retentivity still is associated with improved viscosity in the liquid phase of the dry-set mortar, the actual mechanism for improvement of water retentivity has not been completely explained.
In a copending application Ser. No. 709,176 in the name of Bernett, filed July 27, 1976, now U.S. Pat. No. 4,118,241, it is reported that partial replacement of high viscosity cellulose ethers with low viscosity, cold water soluble polyvinyl alcohols does not cause a reduction in water retentive properties. Therefore, this Bernett patent teaches the water retentivity is not solely a function of the viscosity of the water retentive agent added to the dry-set mortar.
It has now been discovered that the addition of certain organic materials, which in themselves offer no appreciable thickening properties, instead of diluting the liquid phase can improve the water retentive properties of a dry-set mortar. This discovery is quite significant in that the organic liquids which have been found to have these properties are considerably less expensive than the high molecular weight water retentive agents used in dry-set mortars. The addition of these organic liquids does not replace the need to have a higher molecular weight agent, such as a cellulose ether, present, but these organic liquids enable the amount of cellulose ether to be reduced. Hence, for a given amount of water retentive agent, higher water retentive properties can be obtained by the use of the promoters, described herein. Therefore, the promoters make it possible to more efficiently use water retentive agents, particularly those of high viscosity.
In our copending application entitled "Improved Thickeners and Methods for Improving the Effectiveness of Particulate Thickeners of the Soluble Type", filed contemporaneously with the instant application, it is taught that certain organic materials, when added to certain thickeners, such as cellulose ethers, improve the overall thickening properties of the thickeners. That application is incorporated herein by reference. In accordance with the process in that application, the thickener must be pretreated with the organic material and allowed to partially swell prior to its use as a thickener in a liquid composition.
It has been found in accordance with the present invention that improved water retentive properties are obtained in dry-set mortars by using a water retentive agent pretreated with a suitable promoter or by adding the promoter directly to the mortar containing water retentive agent without any pretreatment. Therefore, the promoter of the present invention can be added in situ with the thickener and other components of the dry-set mortar and water. The improved thickening properties as set forth in said copending application do not completely explain the rather surprising results obtained in dry-set mortars, as set forth herein.
A number of prior art references have described the use of certain organic liquids in hydraulic cement compositions, but those compositions are not dry-set mortars and therefore do not contain water retentive agents. For example, in U.S. Pat. No. 3,239,479, triethylene glycol is used as a humectant in a conventional cement composition. In U.S. Pat. No. 3,090,692, triethanol amine is used in making concrete blocks.